Fully developed self-aerated flow in steep chute with various bottom roughness.

Self-aerated open channel flows have been extensively investigated in various physical scales, but comprehensive depiction of air entrainment and air–water flow properties for various invert roughness conditions is limited, sometimes due to the insufficient chute length to reach fully developed aeration. In the present work, an 18 m-long chute was built on a 21.8° sloping river bank, and the aerated flow hydraulics and two-phase flow properties were experimentally measured to the fully aerated region. Three types of bottom roughness were tested, and their effects on flow aeration were discussed. The investigated flow characteristics, including the inception of air entrainment, characteristic flow depths, distributions of air concentration and bubble frequency, flow resistance modification, water level fluctuations, and splash height, were compared with existing model and prototype data and empirical expressions. The results revealed different roles of the uniformly distributed bottom roughness in modifying the two-phase and hydraulic processes and highlighted the importance of flow Reynolds number especially for a mass transfer consideration. [ABSTRACT FROM AUTHOR]